Manufacturers of components for gas turbine engines commonly use brazing as a method for attaching articles together to form the component. These articles frequently have openings. The opening may weaken the ability of the article to resist forces exerted on the article during the brazing process. In addition, molten braze material may flow into these openings during the brazing process and harden during the brazing process, as does the braze used to attach the articles together. The manufacturer must remove the braze which greatly increases the processing time for the article.
One approach for blocking braze material from flowing into an opening is shown in U.S. Pat. No. 5,511,721 issued to Demo and Planchak entitled "Braze Blocking Insert for Liquid Phase Brazing Operations." In Demo, a pre-form insert is disposed in an opening or void in the material. The insert is composed of a refractory metal oxide powder dispersed in a polymeric solid such that the pre-form insert is solid and relatively flexible. The pre-form insert is positioned in the opening or void such that the insert completely fills the void and is retained due to friction generated by an interference fit. A portion of the insert burns off at conventional brazing temperatures leaving a metal oxide powder in the opening that is in a relatively cohesive state. The cohesive metal oxide powder prevents the flow of molten braze alloy into the opening during the brazing operation. However, the metal oxide powder does not have structural strength that would resist forces exerted on the powder. The powder is relatively easy to remove from the opening after the brazing operation.
Another approach for blocking braze material from flowing into an opening is to mask the opening with a layer of oxide material as shown in U.S. Patent 4,023,251, issued to Darrow entitled, "Method of Manufacture of Cooled Turbine or Compressor Buckets." In Darrow, cooling channels covered with a layer of oxide material will not be wet by the molten braze material. This reduces plugging of the covered cooling channels during manufacture by unwanted braze material.
Another approach is to dispose a paste stop-off material such as Braze Stop material available from the Vitta Corporation, Bethel, Conn. Braze Stop material blocks the flow of braze material into the opening. One example of the use of such a Braze Stop material occurred during the manufacture of gas turbine engines by Applicants' assignee.
Applicants' assignee manufactures such engines for military aircraft and for large commercial aircraft. Such engines have a compression section, a combustion section and a turbine section. Working medium gases are flowed through the engine, compressed and then burned with fuel to add energy to the gases. The gases are exhausted form the engine, developing useful thrust for propelling the aircraft.
The compression section includes a compressor stator for directing the working medium gases through the compression section of the engine. The compressor stator has an opening formed in one edge of the stator that adapts the stator to receive a thin sheet metal seal in its assembled condition. The thin seal helps confine the working medium gases to the working medium flowpath as the gases are flowed through the engine. The thin seal is commonly called a feather seal and the slot, a feather seal slot.
The feather seal slot, or opening, weakens the component. Forces are used during brazing to urge the abradable seal material against the braze material. These forces may cause a wall bounding the feather seal slot to deform under the high temperatures and pressures at which the brazing process takes place. This will result in unacceptable deformation of the stator.
A metal shim, such as a stainless steel shim is placed in the feather seal slot during the brazing process to prevent the collapse of the walls bounding the slot as external forces are applied to the slot during the brazing operation. The metal shim may become brazed into the slot despite the presence of the stop-off material. This requires removing the shim by a machining operation such as electro-discharge machining (EDM) or other machining operation, greatly increasing processing time. Nevertheless, the stainless steel shim provides the important function of preventing the walls of the feather seal slot from collapsing during the brazing operation.
Accordingly, scientists and engineers working under the direction of Applicant's assignee have sought to develop other approaches to brazing that block the flow of braze material into an opening in the article, such as cooling passages; and, for some applications, such as brazing near a feather seal slot, that support the article against deformation under the temperature and pressure of the brazing process when required.